Abstract: PROBLEMS The present invention relates to a process for producing a polybenzoxazole polymer and provides a process for producing the polybenzoxazole polymer within a short reaction time. MEANS FOR SOLVING PROBLEMS A process for producing a polybenzazole polymer comprises producing the polybenzazole polymer in a non-oxidizing dehydrating solvent while employing a compound represented by the following general formula (1) as a raw material including a first polymerization step in which polymerization is performed at a temperature of 150° C. or less and a latter polymerization step in which polymerization is performed at a temperature of 200° C.

Abstract: The present invention related to a thermoplastic resin composition for masterbatches, comprising an organophosphorus compound represented by General Formula (1): wherein R1 and R2 each represent an organic group or a halogen atom, and m and n each represent an integer of 0 to 4, and when m or n is an integer of 2 to 4, R1 and R2 may be the same or different, and a thermoplastic resin, wherein the thermoplastic resin composition for masterbatches contains a phosphorus content of 5000 ppm or more. The thermoplastic resin composition for masterbatches can easily be molded even when it has high phosphorus content and thus flame retardancy.

Abstract: The present invention provides a purification method of phosphoric acid, which includes bringing phosphoric acid containing arsenic into contact with hydrogen halide, thereby to remove the arsenic from the phosphoric acid, and a purification method of phosphoric acid, which includes bringing phosphoric acid containing arsenic into contact with hydrogen halide in the presence of a compound capable of generating hydrogen halide under acidic conditions. According to the method for purifying phosphoric acid of the present invention, a completely new method for removing arsenic in phosphoric acid is provided, which does not require a filtration or deaeration step or shows a great amount of residual sodium, unlike a sulfide coagulation method. This method is applicable to high concentration phosphoric acid, particularly polyphosphoric acid, and can be practiced at a low cost.

Abstract: The present invention provides aromatic diamine/aromatic dicarboxylate having the following formula (I) NH2—Ar1—NH2.HOOC—Ar2—COOH  (I) wherein each symbol is as defined in the specification, which is in the form of particles having a median diameter of 5-100 &mgr;m and whiteness of not less than 75. This salt has high polymerizability and preferably has superior storage stability. Therefore, it can be preferably used for the production of polybenzazole that can be formed into a fiber and a film having high strength, high elastic modulus and high heat resistance.

Abstract: A polybenzazoleolybenzazole having a residual content of a BB-PBZ monomer of not more than 0.010 wt %, which is obtained by dehydration polymerization condensation of an AA-PBZ monomer of the formula (I) wherein Ar is a quadrivalent aromatic organic residue and X is O, S or NH, and a BB-PBZ monomer of the formula (II) W—Z—W  (II) wherein Z is an optionally substituted divalent aromatic organic residue and W is a carboxyl group or a group derived from the carboxyl group, which is reactive with —XH in the AA-PBZ monomer. Because the residual content of the BB-PBZ monomer in polybenzazole is not more than 0.010 wt %, a polybenzazole fiber having a small filament denier can be produced stably at a high speed without suffering from thread breakage during the production.

Abstract: The present invention provides aromatic diamine/aromatic dicarboxylate having the following formula (I)

Abstract: A polybenzazoleolybenzazole having a residual content of a BB-PBZ monomer of not more than 0.

Abstract: A method for producing polybenzazole in the presence of iron(II) ion. The polybenzazole obtained by this method can be formed into a highly strong fiber having a high elastic modulus and a heat resistant film. The method enables economical production of polybenzazole having fine tone and high polymerization degree.

Abstract: A method for producing polybenzazole, which comprises reacting a PBZ monomer salt with an AA-PBZ monomer or a BB-PBZ monomer in a non-oxidizing solvent having a dehydrating action to give an oligomer, and adding the AA-PBZ monomer or BB-PBZ monomer, which has not been subjected to the above reaction, to allow reaction with the oligomer, whereby to give a polymer having a desired polymerization degree. According to this method, the polymerization degree of the polymer to be obtained finally and of the polymer during production process can be easily controlled.

Abstract: A method for stabilizing DAR during storage, comprising storing DAR in the presence of a reducing agent having a standard redox potential of not less than -0.20 volt and not more than 0.34 volt, in a proportion of not less than 100 ppm and not more than 10,000 ppm of DAR. The present invention improves storage stability of DAR. This in turn results in easy handling and long-term preservation of DAR. Thus, a high quality polymer PBO can be easily produced and the invention greatly contributes to the industrial field.